A badly charred note with the words "am sorry" was discovered Friday in the torched apartment where investigators suspect a teenager killed his mother and siblings before committing suicide, police said.

New York Police Department spokesman Paul Browne said the note — with only fragments of words and sentences still legible — was found along with a melted butane lighter in the Staten Island home. It was being analyzed to try to determine who wrote it and if it had any significance.

The bodies of Leisa Jones and three of her children were found in their torched apartment early Thursday morning. Her fourth child, a 2-year-old boy, was pulled out alive but died later at the hospital.

Investigators were still trying to determine exactly how Jones and her son died.

Autopsies performed Friday on the pair were inconclusive, said Ellen Borakove, a spokeswoman for the city medical examiner. The inquiries confirmed, though, that two young girls found in the house had died of neck wounds. Police said their throats had been slit. An autopsy on 2-year-old Jermaine Sinclarie determined that he died of smoke inhalation and burns.

Police said the teenager's throat also appeared to have been slit, and investigators theorized that the deaths were the result of a murder-suicide committed by the boy, who had a history of playing with fire.

Investigators, however, haven't completely ruled out the possibility that the mother was the killer, and the medical examiner's office said further study was being done to determine how she and her son died.

The girls' bodies were found along with that of their mother and the 2-year-old in the front room of the family's second-floor apartment. The teenage boy's body was found slumped over a bed in a back bedroom, police said. A straight razor was discovered underneath his body.

The girls were identified as 10-year-old Brittney Jones and 7-year-old Melonie Jones. The 14-year-old son, known previously as C.J. Jones, had tentatively been identified as Raymond Romoy, Browne said.

The teenager recently had been seen setting a fire at a public pool, and neighbors described him lighting paper on fire in front his apartment building in recent days, police said.

Firefighters said they believed the blaze was intentionally set, but their investigation was continuing.

Neighbor Raquel Fagone said she spotted the teenager lighting scraps of paper in front of the building a few months ago.

"I told him not to do that, and he put them out," Fagone said.

Then, early Thursday, she heard a commotion in the family's apartment, directly above hers.

"It sounded like a little child running, upset, in distress, upset, screaming, running around," she said. "I heard a bang and a kind of kaboom."

Fire officials say the blaze started in the apartment and moved through the two-story building's attic space and roof. The tenants in the other three apartments got out safely.

The 32-year-old Jones was from Trinidad and attended beauty school during the day, neighbors said.

Browne said detectives had questioned the 2-year-old victim's father, who was in Baltimore at the time of the fire and is not considered a suspect. The other children have different fathers, he said.